The present invention relates to a flow control device of a helically-shaped intake port of an internal combustion engine.
A helically-shaped intake port normally comprises a helical portion formed around the intake valve of an engine, and a substantially straight intake passage portion tangentially connected to the helical portion. However, if such a helically-shaped intake port is so formed that a strong swirl motion is created in the combustion chamber of an engine when the engine is operating at a low speed under a light load, that is, when the amount of air fed into the cylinder of the engine is small, since air flowing within the helically-shaped intake port is subjected to a great flow resistance, a problem occurs in that the volumetric efficiency is reduced when the engine is operating at a high speed under a heavy load, that is, when the amount of air fed into the cylinder of the engine is large.
In order to eliminate such a problem, the inventor has proposed a flow control device in which a bypass passage, branched off from the inlet passage portion and connected to the helix terminating portion of the helical portion, is formed in the cylinder head of an engine. A normally closed type flow control valve actuated by an actuator, is arranged in the bypass passage and opened under the operation of the actuator when the amount of air fed into the cylinder of the engine is larger than a predetermined amount. In this flow control device, when the amount of air fed into the cylinder of the engine is large, that is, when the engine is operating under a heavy load at a high speed, since a part of air introduced into the inlet passage portion is fed into the helical portion of the helically-shaped intake port via the bypass passage, the flow resistance of the helically-shaped intake port is reduced. Thus, it is possible to obtain a high volumetric efficiency. However, this flow control device merely indicates a basic principle of operation. Therefore, in order to put such a flow control device into the practical use, various problems to be solved are present as to how to reduce the manufacturing time and the manufacturing cost; how to easily manufacture the flow control device; and how to obtain a reliable operation of the flow control device.